Improving the charge storage capacity of carbon materials derived from biomass waste is an important aspect for their practical applications as supercapacitor electrodes. A reasonable design of heteroatom-doped carbon materials derived from industrial distiller 's grains can significantly enhance the efficacy of the supercapacitor. Therefore, a distiller's grain-derived (DG) N/O self-doped activated carbon (DG-5-X) was developed for use in supercapacitors. The incorporation of heteroatoms into porous carbon materials can facilitate enhanced electrode-to-electrolyte interaction resulting in improved pseudo-capacitance, thereby enhancing the electrochemical performance. A remarkable 345.2 F g−1 specific capacitance was demonstrated in a three-electrode system employing DG-5–6 (with N and O heteroatom contents of 1.62 % and 19.27 %, respectively) as the electrode in a 6 M KOH electrolyte solution (at 1 A g−1). In addition, a symmetric coin-type supercapacitor (SSC) device was developed, which demonstrated excellent cyclic stability and a competitive energy density of 12.2 Wh kg−1 (at a 348.8 W kg−1 power density). SSC retained 95.6 % of the capacitance after 5000 cycles at 5 A g−1. In summary, the distiller’s grains as a raw material show great potential in the development of carbon-based energy storage materials that display outstanding electrochemical performance.